A reversed-phase HPLC method was developed for the determination of maesopsin, a fliavonoid, in the xylem parts of the traditional Tibetan medicinal herb Shengdeng (Rhamnella gilgitica). An ODS column was used and the mobile phase was methanol-water (28:27) with 0.05 mol/L KH2PO4 (pH4). The detection wavelength was UV 290 nm. The recovery was 98.9% (RSD = 2.1%, n = 6) and the content of maesopsin in Shengdeng was 1.02% (RSD = 0.52%, n = 3).